The present invention relates to a driving system for pneumatically driven type pumps such as a blood pumping device and the like.
As a driving system of this type there has been known, for example, a driving system of such a construction as shown in FIG. 1, in which indicated at numeral 1 is a compressor, at 2 a vacuum pump, at 3 a positive pressure tank, at 4 a negative pressure tank, at 5 an electromagnetic change-over valve and at 6 a pressure reducing valve.
The interior of the positive pressure tank 3 is maintained at a predetermined positive pressure by means of the compressor, while the interior of the negative pressure tank 4 is maintained at a negative pressure by the vaccum pump 2. Positive and negative pressures alternately act on (pressurize and suck in) and drive a pneumatically driven pump 8 such as a blood pumping device provided at a driving pressure outlet 7 from the positive pressure tank 3 and negative pressure tank 4 through the electromagnetic change-over valve 5.
According to the above driving system, in order to operate the pneumatically driven type pump 8 as per the rating by supplying predetermined pressures thereto, it is necessary that the capacity of the positive pressure tank 3 and that of the negative pressure tank 4 be set at a value, for example, several ten times (40-50 times) as large as that of the pneumatically driven type pump 8. This is for the following reason.
When the positive pressure tank 3 is opened by the electromagnetic change-over valve 5, the pressure in the tank 3 drops, while when the negative pressure tank 4 is opened, the pressure in this tank 4 rises. These pressure drop and rise are negligible if the capacities of the tanks are sufficiently large. However, if the tank capacities are not sufficient, the ratios of such pressure drop and rise are large. Since the response speed of the pressure reducing valve 6 is generally not so high, the valve 6 cannot immediately compensate for such pressure drop and rise, so that the pressure waveform at the driving pressure outlet 7 and that at the pneumatically driven type pump 8 are influenced by such pressure drop and rise. The solid line A in FIG. 2 shows a pressure waveform influenced by the pressure drop.
In FIG. 2, the alternate long and short dash line B represents an ideal waveform free from pressure drop, the dotted line C represents a pressure curve in the positive pressure tank 3 in the case of gas being not replenished, and the alternate long and two short dashes line D represents a pressure curve under operation of the pressure reducing valve 6.
In the case where the flow path between the driving pressure outlet 7 and the pneumatically driven type pump 8 is long and is formed by a flexible hose of a small diameter, the pressure waveform in the pneumatically driven type pump 8 is influenced by the intratube pressure and tube deformation in addition to the pressure drop and is as if it had been passed through a low-pass filter as shown in FIG. 3.
Particularly in a blood pumping device, it is necessary that the blood pressure curve exhibited by the blood pump be as approximate as possible to that of a natural heart and, most ideally, identical with the latter. To this end, in driving systems for blood pumping devices, the foregoing pressure drop and rise must be kept to a minimum, so it is necessary that the capacities of the tanks 3 and 4 be set sufficiently large.
Thus, because of the necessity of making the capacities of the tanks 3 and 4 sufficiently large, the greater part of the driving system is occupied by the tanks 3 and 4, that is, it is difficult to attain reduction of size.